21. A study of the association between whether a smoker (yes. nor and whether have had some form of cancer (yes, no) has odds ratio 1 1 for subjects of age less than 30. 2.4 for subjects of age 30 to 50, and 4.3 for subjects of age over 50.

a) Identify the response variable, explanatory variable. and conuol variable. and interpret the associations.

b) Does the study show evidence of interaction? Explain.